Tumor control and respiratiory function after stereotactic irradiation (STI) for primary and metastatic lung cancer

The Role of Radiation Therapy in Thoracic Tumors

Radiation plays an important role in the treatment of thoracic tumors. During the last 10 years there have been several major advances in thoracic RT including the incorporation of concurrent chemotherapy and the application of con-formal radiation-delivery techniques (eg, stereotactic RT, three-dimensional conformal RT, and intensity-modulated RT) that allow radiation dose escalation. Radiation as a local measure remains the definitive treatment of medically inoperable or surgically unresectable disease in NSCLC and part of a multimodality regimen for locally advanced NSCLC, limited stage SCLC, esophageal cancer, thymoma, and mesothelioma.

Early stage medically inoperable non-small cell lung cancer

A nihilistic approach to the treatment of patients with medically inoperable, early stage non-small cell lung cancer (NSCLC) is not warranted. Despite the frequency of comorbid medical illness in patients with medically inoperable NSCLC, lung cancer progression is the major cause of morbidity and death. Although expectations for cure are reduced compared to good-risk patients (eg, adequate pulmonary reserve), modest long-term survival rates of patients have been reported, after definitive therapy. A comparison of radiotherapy and limited resection is difficult because of the lack of randomized data and the selection bias inherent in retrospective reports. For example, patients treated with surgery have peripheral lesions, undergoing rigorous staging compared to patients treated with radiotherapy. In a multidisciplinary thoracic program, patients are counseled on the options of sublobar resection and conformal radiotherapy. The efficacy of adjuvant radiotherapy, after limited resection, in reducing local recurrence in patients with medically inoperable NSCLC is unclear. However, adjuvant radiotherapy may be considered if a postoperative target volume can be defined, particularly if resection margins are narrow. Considering the benefit of chemoradiotherapy for patients with locally advanced disease, combination therapy is administered to patients with good performance status and large (eg, > 4 cm) primary lesions, although combined therapy may increase the potential for pulmonary toxicity in patients with baseline pulmonary dysfunction. Prospective data are becoming available to define the value of treatment alternatives for patients with medically inoperable NSCLC. The Cancer and Leukemia Group B completed a phase II study of thoracoscopic wedge resection and postoperative radiotherapy, whereas a phase I trial of dose-intensive accelerated conformal radiotherapy is ongoing. Trials involving systemic therapy for patients with medically inoperable NSCLC should be developed.

Hypofractionated irradiation for non-small cell lung cancer

Large radiation fractions are an effective way of killing tumour cells but have generally been avoided in curative treatment of patients because of concerns of a disproportionate increase in late normal tissue toxicity. Radiobiological modelling of the effect of radiation on lung tumours and late-reacting normal tissues, which are more sensitive to large radiation fractions, has been undertaken. The biological effect of radiation on tumours is increased as the overall treatment time is shortened but this is not true for late-reacting normal tissue. Sample data are shown in which the relative increases in radiation effect on the tumour and late-reacting normal tissues are similar after hypofractionation. A favourable therapeutic ratio can be achieved because the bulk of normal tissue will receive a lower dose of radiation at a lower dose per fraction than the tumour, especially with current techniques where the volume of normal tissue irradiated can be sharply reduced. The clinical evidence confirms that lung toxicity is volume-dependent. It is the small Stage I and II tumours which are most likely to benefit from hypofractionated regimens, as the volumes to be treated are smaller and they have a lower incidence of distant metastases. Patients with Stage III tumours with favourable prognostic factors are nowadays treated with combined chemotherapy and radiotherapy and so for this group more conservative hypofractionation regimens are being explored. However, more advanced tumours may be treated with hypofractionation to lower total doses to achieve palliation and a modest degree of survival benefit.